DE4141775A1 - Electronic circuits mfr. - using temporary substrate for assembly and fixing with cast epoxy] resin - Google Patents

Abstract

Electronic circuit is mfd. by applying conductor track paste (4) on a plastic film (2) coated with parting agent as temporary support and then placing electronic components (6) so that their connections (8) adhere to the paste, which is cured by heat. A mould is placed around the substrate and a cast material, pref. an epoxy resin (12), is poured in and cured. The temporary substrate is then recured. Multi-layer circuits can also be mfd. ADVANTAGE - No printed circuit board, components can be adjusted before fixing with resin.

Description

The invention relates to a method for manufacturing an electronic circuit with conductor tracks and electronic components.

In a most common, known method of this type, electronic circuits with printed conductors arranged on a circuit board and electronic components are produced. This known method comprises the following steps:
First, a plate must be made, which is generally used epoxy resin. This stable carrier is usually coated on both sides with a very thin copper layer. Then the holes for the plated-through holes and / or for the connection of the end legs of the electronic components are drilled. The bores are then pretreated electrochemically to produce the desired electrical connections between the two copper planes. Next, a photosensitive layer is applied to the copper on both sides of the plate. With the help of a slide film, the conductor tracks, the plated-through holes and the soldering points are imaged. The photographic material is removed at those points where conductor tracks are to be created. The exposed copper surfaces are then galvanically reinforced. Just in case the vias are formed in the corresponding holes. A solder (usually consisting of ZnPb) is then applied to the copper-reinforced surfaces as an etching resist. The next step is to remove the photo layer. Now the unnecessary copper surfaces are etched away. The tin is then completely removed so that a solder mask can then be applied. In order to protect the now exposed copper surfaces from corrosion, but also to achieve better conductivity, the copper surfaces are now coated with a suitable solder.

Then the components are assembled. The components are generally soldered to the connection lines electrically connected. SMD components are in an intermediate step and then in a wave soldering system, or the solder is in  Form of a paste printed in the screen printing process and soldered in a reflow process.

This known manufacturing method for an electro African circuitry not only requires a particularly large number Manufacturing steps, but also comparatively much Material that ver for the manufacturing process must be used, but for the one then manufactured electronic circuit for the most part no longer ge is needed.

Because of the aforementioned circumstances, this is known Process for the production of electronic circuits time consuming and due to the multitude of process steps requires very high investments in production equipment. It is also a big waste characterized by material which is for the actual Function is no longer needed. especially the Manufacture of multilayer or multilayer circuits is very time, cost and material intensive, because all che process steps have to be run through several times.

Another problem is environmental pollution due to the resulting process waste such as alkalis, acids, Copper, tin, lead, residues of the photo mask etc. Some of these substances are recycled leads, which on the one hand increases the effort and on the other hand however, no complete recovery of the used ones Fabrics. A significant part remains as Hazardous waste, which is difficult to dispose of prepares. Another serious problem is the resulting process vapors, which only with great effort  can be dissipated, one cannot be ruled out eating, health impairment of the staff nonetheless remains.

Another disadvantage of the known method is in that the electronic circuitry thus created can only be tested in the final state. A Subsequent repairs are not possible unless that missing or broken connections by means of restore lines or cables to be attached externally be put what, on the one hand, no more than a Provi sorium and the requirements of practice are rare is sufficient and secondly is very time consuming.

It is therefore an object of the invention to provide a method for Creating an electronic circuit to create which is easier and cheaper to do, none Material wastage, environmentally friendly and a necessary correction of the circuit allowed without much effort.

This problem is solved with a method which is characterized by the steps

• - For the formation of the conductor tracks on the for this seen places on electrically conductive material releasably apply a carrier,
• - The carrier with the electronic components to be releasably equipped so that their connections with the applied electrically conductive Material formed conductor tracks in contact gen, and
• - On the carrier curable casting compound in such a way bring that the traces and components of the casting compound are surrounded and a substantially  Chen firm connection between the casting compound and the electrically conductive material of the conductor tracks will be produced.

A major advantage of the inventive method rens is that the conventional board on which the conductor tracks and the electronic components were arranged, is replaced by a casting compound, the surrounds and receives the conductor tracks and components and this after hardening - like the board at the state of Technology - carries and fixes to each other, and that before Applying the casting compound all electrical connections as well as electronic components in one only "loose" structure on the carrier linked together are, which makes it particularly easy to test given is. In addition, after a circuit test corrections (e.g. rectification of circuit break tests, adding conductor tracks or exchanging Components) particularly easily and without major opening Perform wall on the support. This was against State of the art not just, but only with increased effort possible, since such corrections only of the already completed board could. Only when the desired overall function of the electronic circuit completely and positively about checked and thus has been ensured by Applying the molding compound is a substantially stable and homogeneous overall structure, whereby by the Casting compound as a shaping component not only the ge wanted mechanical stability, but also protection from unwanted environmental influences and heat loss leadership is achieved.  

Another significant advantage of the invention The procedure is that, in contrast to the state technology with significantly fewer work steps is coming. This will not only make elek tronic circuits simplified and accelerated, but it also means the effort and thus the Costs significantly reduced, which makes the fiction Moderate manufacturing process especially for small other quantities is economically interesting. Except therefore the method according to the invention does not require mate rial waste like in the prior art, but it exactly the amount of material is required that required to build the electronic circuit is. There is no excess material that is gone etched or otherwise removed. So he the method according to the invention produces no waste which would pollute the environment and special protection and Recycling measures required. This is especially true also for the etching required in the prior art process to protect the health of personnel made special additional protective measures necessary and is no longer required in the invention. There accordingly the value of the material used compared to State of the art is much lower with With the help of the invention further cost savings are achieved will.

With the help of the inventive method Herge provided electronic circuit is particularly resistant to harsh environmental conditions such. B. aggressive atmosphere, moisture and mechanical shocks without special additional measures as in the prior art technology are required. The mechanical properties of the hardened casting compound can be improved by inserting fine glass fabric. In particular, the addition of glass fabric in several layers prevents any deformation during and after curing. The thermal properties can be improved by the targeted addition of fillers that have a high thermal conductivity with good electrical insulation properties. The fillers should preferably consist of Al ₂ O ₃ or AlN. In this way he will improve the power dissipation.

The carrier is preferred after the casting compound has hardened at least in those places where the ladder form external connections, but in general completely removed so that it is only used as a means of solving Fix the electrically conductive mate to be applied rials for the formation of the conductor tracks and the to be arranged serves electronic components and then for the manufacture of the next electronic circuit can be reused. With an advantageous Further development, the carrier has material on which the Casting compound and / or the electrically conductive material of the Conductors are only releasably liable.

In general, the carrier should be made of electrical insulation be made of material.

Another currently preferred Execution will be carried out before applying the cast mass placed in a form so that the ge of the form formed cavity from which the traces and building elements te supporting side of the carrier is limited and will this cavity is filled with the casting compound. The advantage this version consists on the one hand in that only  much casting compound is used, as for the application is needed. Another advantage of this version lies in the fact that the conductor tracks and components receiving body made of casting material with a any shape according to the shape used can be provided; for example, is not just like with the boards in the state of the art an essentially planar conceivable, but any three-dimensional shape and polygonal structure. There by it is possible to use the circuit with simple the exact location of the location ratios or to adapt to a given housing or, for example, the casting mass body directly as Form housing wall. Generally the shape removed after curing of the casting compound and for the Making the next electronic circuit like the used.

Another currently preferred embodiment of the The method according to the invention is characterized in that that to form the conductor tracks electrically conductive Mass, in particular conductor paste, in pasty form is applied to the carrier, then the carrier equipped with the components and only after drying NEN / hardening of the electrically conductive mass, the casting mass is applied to the carrier. With such in itself known electrically conductive masses such as in particular Conductor pastes can be used in particular make it easier. Generally exist such pastes made of adhesive base material, the conductive Contains particles that are only in the hardened state come into contact with each other and thus a conductive Establish a connection.  

In a further development of this version are Basic materials of the electrically conductive mass and the casting mass similar or identical. This is a special the intimate connection between the conductor tracks and the Cast mass achieved, which makes a substantially homo overall structure. In addition, a be particularly high adhesive strength between the conductor tracks and the components on the one hand and the casting compound on the other on the one hand, through which the conductor tracks and components be fixed. The basic materials generally exist from polymers such as B. epoxy.

It is particularly useful to use the electrically conductive Material for forming the conductor tracks on the carrier, especially with the help of a screen printing process to press. This measure allows the conductor rail not only in a particularly simple and quick way form, but also just simple devices such as B. a screen printing machine required Acquisition does not cause high costs.

To remove the carrier particularly easily should, this should be before applying the conductor NEN and components with a release agent, which preferably contains silicone.

A particularly simple and quick connection of the Components with the conductor tracks result from that the connections of the components with the conductor tracks be glued in an electrically conductive manner. If electrical conductive pasty mass is used, it should glue contain substance, which means additional measures to open wearing glue is eliminated.  

Electronic circuits with conductors are very common membranes made in a multilayer arrangement. As before was mentioned at the beginning, were in the manufacture of the conventional multilayer boards a lot of work steps necessary for each order of a layer not only required a lot of time, but also high costs caused. Another disadvantage came with the state of the Technique added that the adjustment of each layer-Trä against the next new layer to be applied over the circuit board due to not being fully removable closing tolerances in the fitting holes only with be of limited accuracy could be performed the resolution of the multilayer structure was limited. In contrast, with the help of the invention faster, simpler and therefore cheaper Her position of an electrical circuit with conductor tracks possible in multilayer arrangement. This is fiction moderately achieved in that after each application of a Location of conductor tracks and, if applicable, components on them Layer an electrically insulating layer applied the next layer of ladder paths and possibly components is applied. While such an alternating application of conductor track lay and insulating layers, which is preferably with the help of printing processes, only those Fit holes of the carrier used and thus the carrier for all layers in an identical position adjusts what is advantageous to the resolution of the multilayer structure has an effect since, in addition to the advantage achieved according to the invention a significant reduction in the number of work steps a much more precise arrangement and finer training the conductor tracks can be achieved.  

The insulating layer is expediently covered by Applying casting compound or non-conductive ground mass from the for the formation of electrical conductor tracks used electrically conductive mass formed.

At those points where conductor tracks from neighboring beard layers are electrically connected to each other should be easy in the intermediate layer a window formed or printed. Now the next conductor layer on this insulating layer placed, the conductor tracks arrive in the area of the Window in electrical contact with each other.

Before attaching the conductor tracks and components should have an electrically insulating layer on the backing ger be applied. This is especially true of Advantage if the carrier at the end of the manufacturing process ses is removed again, so that the conductor tracks and Connections of the components are not exposed, but from this electrically insulating layer are protected. This layer should also expediently be opened carry casting compound or non-conductive ground mass from the for the formation of electrical conductor tracks used electrically conductive mass are formed.

The carrier should preferably be made of a plastic film exist, the production of which does not entail high costs gently.

The casting compound and / or the expediently should electrically conductive mass consist of a material, which under the influence of heat or IR or UV radiation lung hardens.

Preferred embodiments of the Invention with reference to the accompanying drawings shown. Show it:

Figures 1 to 5, the manufacturing steps of an electronic circuit in cross section.

Figure 6 which is still in a mold and on an intermediate carrier, already prepared electronic circuit of a modified embodiment in cross section.

Fig. 7 is a section of a multilayer arrangement of two conductor tracks in plan view;

Fig. 8 shows the arrangement of Figure 7 in cross section.

Fig. 9 is a section of a multilayer arrangement of three circuit traces with a crossing point in plan view; and

Fig. 10 shows the arrangement of Fig. 9 in cross section.

The manufacture of an electronic circuit according to the invention is described below with reference to FIGS. 1 to 5. The circuit described in the following example is shown for reasons of clarity only with two conductor tracks and an elec tronic component, which may consist of a chip, for example. In reality, such a circuit is much more complicated and includes a variety of conductor tracks and Bauelemen th.

An intermediate carrier 2 is used for the production of the electronic circuit, which, for example, as shown in the figures, can consist of a plastic film. On the side on which the conductor tracks and the electronic components are to be arranged, the intermediate carrier 2 is coated with a separating agent, which preferably contains silicone.

To form the conductor tracks 4 , conductor paste is used in the exemplary embodiment described here. The known conductor track paste consists of an adhesive base material which contains the finest conductive particles. In the pasty state, the conductor paste is not conductive because there are slight gaps in the base material between the conductive particles. During the hardening of the conductor paste, the conductive particles come into electrical contact with one another and form a conductive bridge, so that the conductor paste is now conductive. The base material of the conductor paste consists of a polymer, in particular an epoxy resin. Instead of conductor paste, pa-shaped or otherwise applicable resistance material can also be used, specifically where resistors are to be formed, so that corresponding discrete components can be dispensed with.

At those points at which conductor tracks 4 are to be formed, the conductor track paste is now applied in pasty form to the intermediate carrier 2 in the form of a track, as can be seen schematically in FIG. 1. In general, the conductor paste z. B. with the help of a screen printing device on the intermediate carrier 2 .

After the formation of the conductor tracks 4 on the surface of the intermediate carrier 2 , the latter is now equipped with the electronic components, of which the electronic component 6 is shown as an example in FIG. 2. In this case, the connections 8 of the component 6 are glued to the conductor tracks 4 in the exemplary embodiment presented, at a time at which the conductor paste being carried is still pasty and adhesive, so that the adhesive effect is achieved by the adhesive contained in the conductor paste. By gluing with the conductor tracks 4 , the electronic component 6 is already sufficiently fixed on the intermediate carrier 2 for the electrical function.

After all Lei tracks 4 and electronic components 6 have been applied to the intermediate carrier 2 and the conductor paste has been hardened under the influence of heat or IR or UV rays in the manner described above, the electronic circuit is already made so far that it can be checked and tested. If an error is found in the circuit, changes can be made to the circuit without any problems, in general through changes in the position of the conductor tracks or in the position and in the connections of the electronic components.

As can be seen in FIG. 3, a mold 10 is then placed on the intermediate carrier 2 , so that the cavity 11 formed by the mold 10 is delimited by the side of the intermediate carrier 2 carrying the conductor tracks 4 and the electronic components 60 and the conductor tracks 4 and the components 6 receives. This cavity 11 is then filled with a casting compound 12 . This casting compound is in liquid form and can be cured, for example, under the influence of heat or IR or UV radiation. The casting compound 12 should contain the same base material as the conductor tracks 4 forming the conductor tracks, so that an intimate, homogeneous connection is achieved between the casting compound 12 and the conductor tracks 4 , whereby a strong adhesion of the conductor tracks 4 to the casting compound 12 after it has hardened arises. In particular, good adhesion is obtained by enlarging the surface by forming a sieve structure. With the help of the casting compound 12 , all conductor tracks 4 and electronic components 6 are thus fixed to one another and to the casting compound, so that the casting compound 12 takes on the same carrier function as the circuit board in the prior art.

In the arrangement shown in Fig. 3 arises after hardening of the casting compound 12 , the conductor tracks 4 and the electronic components 6 containing, platteniform body. Nevertheless, the intermediate carrier 2 and the mold 10 can also be designed such that the body can take on any three-dimensional or polygonal shape. The material of the casting compound 12 can also be chosen so that after its hardening the body remains elastic.

After the casting compound 12 has hardened, the intermediate carrier 2 is removed (cf. FIG. 4). This is made possible by the fact that the intermediate carrier 2 is coated with a release agent; alternatively, it can also consist of a material on which the conductor paste and the casting compound 12 do not adhere firmly, but releasably. Subsequently, the mold 10 is also removed, so that a structure made of hardened casting compound 12 and conductor tracks 4 and components 6 contained therein remains as a finished circuit, as shown in FIG. 5.

In Fig. 6 is still on the intermediate carrier 2 sit zende and surrounded by the form 10 electronic scarf device shown in a further embodiment, which differs from the embodiment of FIG. 5 in that the conductor tracks 4 from an electrically isolating end Cover layer 14 are protected. The electrically insulating cover layer 14 also consists of casting mass and is applied to the intermediate carrier 2 before the conductor tracks 4 are produced.

With the method described by way of example with reference to FIGS. 1 to 5, a multilayer circuit can also be produced. After applying a layer of conductor tracks and possibly components, an electrically insulating layer is applied to this layer, on which the next layer of conductor tracks and possibly components is subsequently applied.

In Figs. 7 and 8 is an example an arrangement of two superimposed conductor tracks 4 a and b shown 4, which are separated by an intermediate layer 16 iso-regulating. After application of conductor paste to form the lower conductor 4 b on the electrically insulating layer 14 , the further insulating layer 16 is applied, on which the conductor 4 a is then brought up in the next layer. To form a homogeneous unit, the insulating layers 14 and 16 and the casting compound 12 are made of the same material. Depending on the application, the insulating intermediate layer 16 can extend over the entire surface of the underlying layer or, as is shown in FIGS. 7 and 8, only over a part.

In FIGS. 9 and 10, the same arrangement is shown as an example as shown in Figs. 7 and 8, but using 5 to be formed between the conductor track 4 a in the upper layer and a conductor track 4 c in the lower layer a connection point. For this purpose, the isolating de intermediate layer 18 is provided with an opening or window 20 . The intermediate layer 20 is applied to the lower layer with the conductor tracks 4 b and 4 c that the part of the conductor track 4 c is exposed through the window 20 at the later connection point 5 . Subsequently, the conductor track 4 a is applied to the insulating intermediate layer 18 in such a way that it extends over the window 20 and there comes into contact with the underlying conductor track 4 c to form the connection point 5 .

In the arrangements shown in FIGS . 7 to 10, for the sake of clarity, only two superimposed layers with conductor tracks are exemplary. A larger number of layers is usually provided in a multilayer arrangement, the layers and insulating layers being applied in succession in an alternating sequence. There are only pass holes in the intermediate carrier 2 (not shown in FIGS . 7 to 10) in the application device, which preferably consists of a screen printing machine before, and thus the intermediate carrier 2 is kept from layer to layer in an identical, unchanged position, thereby the Production of multilayer structures becomes very easy. In addition, it should also be pointed out that with the previously described production method, not only conductor tracks, but also construction elements can be arranged in one layer, so that not only the conductor tracks but also the components can be arranged in a multilayer arrangement. SMD components are particularly suitable for this.

Claims (23)

1. A method for producing an electronic circuit with conductor tracks ( 4 ) and electronic construction elements ( 6 ), characterized by the steps,

• - In order to form the conductor tracks ( 4 ), electrically conductive material is releasably applied to a carrier ( 2 ) at the locations provided for this purpose,
• - The carrier ( 2 ) with the electronic components ( 6 ) to be releasably equipped such that their connections se ( 8 ) come into contact with the conductor tracks ( 4 ) formed by the applied electrically conductive material, and
• - Apply to the carrier ( 2 ) curable casting compound ( 12 ) in such a way that the conductor tracks ( 4 ) and the components ( 6 ) from the casting compound ( 12 ) surround who and a substantially firm connection between the casting compound and the electrically conductive Material of the conductor tracks ( 4 ) is produced.

2. The method according to claim 1, characterized in that after curing of the casting compound ( 12 ), the carrier ( 2 ) is removed. 3. The method according to claim 1 or 2, characterized in that the carrier ( 2 ) consists of a material to which the casting compound ( 12 ) and / or the electrically conductive material of the conductor tracks ( 4 ) adheres only releasably. 4. The method according to any one of claims 1 to 3, characterized in that the carrier ( 2 ) is made of elec trically insulating material. 5. The method according to any one of claims 1 to 4, characterized in that

• - The carrier ( 2 ) before applying the casting compound ( 12 ) is placed in a mold ( 10 ) so that the cavity ( 11 ) formed by the mold ( 10 ) from which the conductor tracks ( 4 ) and components ( 6 ) supporting side of the carrier ( 2 ) is limited, and
• - This cavity ( 11 ) is filled with the casting compound ( 12 ).

6. The method according to claim 5, characterized in that after curing of the casting compound ( 12 ), the mold ( 10 ) is removed. 7. The method according to any one of claims 1 to 6, characterized in that to form the conductor tracks ( 4 ) electrically conductive composition, in particular conductor paste, is applied in paste form to the carrier ( 2 ), then the carrier ( 2 ) with the Components ( 6 ) and the casting compound ( 12 ) is applied to the carrier ( 2 ) only after the electrically conductive compound has dried and hardened. 8. The method according to claim 7, characterized in that the basic materials of the elec trically conductive mass ( 4 ) and the casting compound ( 12 ) are similar or identical. 9. The method according to claim 8, characterized in that the base material is a polymer, is in particular an epoxy resin. 10. The method according to any one of claims 1 to 9, characterized in that the electrically conductive material ( 4 ) on the carrier ( 2 ), in particular with the aid of a screen printing process, is printed. 11. The method according to any one of claims 1 to 10, characterized in that the carrier ( 2 ) prior to bringing on the conductor tracks ( 4 ) and components ( 6 ) is provided with release agent. 12. The method according to claim 11, characterized in that the release agent is silicone contains. 13. The method according to any one of claims 1 to 12, characterized in that for connecting the components ( 6 ) with the conductor tracks ( 4 ), the connections ( 8 ) of the components ( 6 ) with the conductor tracks ( 4 ) are electrically conductively bonded. 14. The method according to claims 13 and 7, characterized in that the electrically conductive mass ( 4 ) contains adhesive. 15. The method according to any one of claims 1 to 14, for the production of an electronic circuit in multilayer arrangement, characterized in that in each case after applying a layer of conductor tracks ( 4 b; 4 b, c) and possibly components on this layer an electrically insulating layer ( 16 ; 18 ) is applied, on which the next layer of conductor tracks ( 4 a) and possibly components is then applied. 16. The method according to claim 15, characterized in that the insulating layer ( 16 ; 18 ) is formed by applying casting compound. 17. The method according to claim 15 or 16, characterized in that the insulating layer ( 16 ; 18 ) is printed. 18. The method according to claims 15 and 7, characterized in that the insulating layer ( 16 ; 18 ) is formed by a non-conductive component of the electrically conductive mass. 19. The method according to any one of claims 15 to 18, characterized in that at those points ( 5 ) at which conductor tracks ( 4 a, 4 c) are to be electrically connected to one another from adjacent layers, a window in the intermediate layer ( 18 ) ( 20 ) is formed. 20. The method according to any one of claims 1 to 19, characterized in that before the application of the Lei terbahnen ( 4 ) and components ( 6 ) an electrically insulating layer ( 14 ) is applied to the carrier ( 2 ). 21. The method according to claim 20, characterized in that this layer ( 14 ) is formed by applying casting compound. 22. The method according to claims 20 and 7, characterized in that this layer ( 14 ) is formed by a non-conductive component of the electrically conductive mass. 23. The method according to any one of claims 1 to 22, characterized in that the carrier ( 2 ) consists of a plastic film.